The law of universal gravitation states that a gravitational force exists between all objects in the universe. this force is directly proportional to the masses of the two objects and inversely proportional to the distance between them. this principle is a law because a. it is contradictory to ideas proposed by other scientists. b. it is subject to change as new technology and evidence emerges. c. it cannot be tested through a controlled scientific investigation. d. it has been demonstrated to be without exception under certain stated conditions.

D. it has been demonstrated to be without exception under certain stated conditions.

Explanation:

A Law is an affirmation (something established) based on repeated long-term observation of a phenomenon that has been studied and verified.  

That is: A law is present in all known theories and therefore is considered universal. In addition, a law can not be refuted, nor changed, because its precepts have been proven through various studies.  

Unlike theory, which is the set of rules and principles that describe and explain a particular phenomenon and is subject to changes as new evidence emerges that gives meaning to it.  

Then, based on what is explained above, the law of universal gravitation is a statement that exists because it was rigorously tested and verified, therefore it can not be refuted.